Multicomponent fibers capable of thermally induced shape recovery and the making thereof

ABSTRACT

Multicomponent fibers and films, which can be deformed at room temperature and exhibit thermally-actuated shape recovery properties and methods of their use are provided.

REFERENCE TO RELATED APPLICATION

This application is a PCT International Application which claims thebenefit of U.S. Provisional Application No. 61/709,787, filed Oct. 4,2012, the content of which is herein incorporated by reference in itsentirety.

BACKGROUND

Shape memory is the ability of a material to recover its original shapeafter temporary deformation upon application of an external stimulus.Materials exhibiting shape memory also are referred to asself-repairing, stimuli-responsive, smart, and intelligent (Lendlein andKelch, 2002). Various external stimuli, including, but not limited to,heat, solvation, light, and other electromagnetic fields, can induce achange in material shape.

Polymeric materials capable of shape memory possess significantadvantages over inorganic shape-memory alloys (SMAs). Shape-memorypolymers (SMPs) can be manufactured at a lower cost and under scalabletemperature and pressure conditions, while remaining applicable to awide range of end uses (Behl and Lendlein, 2007). The fabrication ofshape-memory devices from polymeric materials known in the art, however,often involves multistep processing mechanisms that could limit theapplicability and the scalability of the technology.

SUMMARY

In some aspects, the presently disclosed subject matter provides amulticomponent fiber or film comprising at least one component capableof forming a physically-crosslinked network and at least a secondcomponent capable of transitioning in response to a thermal stimulus,wherein the two components have strong interfacial adhesion; and whereina temperature associated with the second component capable oftransitioning in response to a thermal stimulus is lower than atemperature required to disrupt the molecular network of the componentcapable of forming a physically-crosslinked network.

In particular aspects, the fiber or film comprises at least two co-spunor co-extruded components configured in a core component-sheathcomponent cross-sectional geometry, wherein one core component comprisesa thermoplastic elastomer capable of forming a physically-crosslinkednetwork and the sheath component comprises a polyolefin capable oftransitioning in response to a thermal stimulus, and wherein the fiberor film can be deformed from an original shape, retain a temporaryshape, and subsequently return to its original shape in response to athermal stimulus.

In certain aspects, the core component comprises a styrenic blockcopolymer, for example, poly(styrene-b-butadiene-b-styrene) (SBS),poly(styrene-b-isoprene-b-styrene) (SIS),poly[styrene-b-(ethylene-co-propylene)-b-styrene] (SEPS), orpoly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS). In certainaspects, the sheath component comprises a linear low densitypolyethylene (LLDPE). In particular aspects, the core componentcomprises SEBS and the sheath component comprises LLDPE. In yet moreparticular aspects, the sheath component has a melting point lower thanthe upper glass transition temperature of the network-forming corecomponent.

In some aspects, the presently disclosed fibers can be used as a thermalactuator in a deployable device. In other aspects, the presentlydisclosed subject matter provides an article comprising one or more ofthe presently disclosed shape-memory multicomponent fibers. Sucharticles can be used in or can include diapers, waist bands, stretchpanels, disposable garments, medical or personal hygiene articles, andfilters; or, in yet other aspects, a hinge, a truss, an antenna, a solarpanel, or an optical reflector; or in still yet other aspects, a formfitting material, self-sealing packaging, a smart textile, and anintelligent fiber; or in yet other aspects, a wound closure suture, avascular stent, a bone-setting sleeve, or a drug delivery device.

Certain aspects of the presently disclosed subject matter having beenstated hereinabove, which are addressed in whole or in part by thepresently disclosed subject matter, other aspects will become evident asthe description proceeds when taken in connection with the accompanyingExamples and Figures as best described herein below.

BRIEF DESCRIPTION OF THE FIGURES

Having thus described the presently disclosed subject matter in generalterms, reference will now be made to the accompanying Figures, which arenot necessarily drawn to scale, and wherein:

FIG. 1 shows a schematic of shape-memory materials responsive to heat(Prior Art);

FIG. 2 shows shape memory with multiple stages of recovery (Prior Art;Xie, 2010);

FIG. 3 shows a schematic diagram of Type II SMPs involving crystallinemicro-domains (Prior Art; Behl and Lendlein; 2007);

FIG. 4 shows a schematic representation of the stress-strain curvecharacteristic of a thermally-stimulated SMP network during cyclicloading (Prior Art);

FIG. 5 shows: (A) a knot that is tightened by heating the fiber (toabout the human body temperature) so that optimal force is applied onthe closed wound; and (B) SMP material as a smart suture for woundclosure application (Prior Art; Lendlein and Langer, 2002);

FIG. 6 shows: (A) the performance of a SMP hinge, B) the components ofthe SMP hinge showing the SMP composite parts (Prior Art; Lan et al.,2009);

FIG. 7 shows actuation using SMP hinges in deployable devices (PriorArt; Lan et al., 2009);

FIG. 8 shows TEM images of TPEs exhibiting lamellar (left), cylindrical(middle) and spherical (right) morphologies. The scalemarker correspondsto 200 nm in the left and middle images, but 100 nm in the right image(Prior Art; Krishnan et al., 2010);

FIG. 9 shows heating cycles for shape-memory fibers with reproduciblerecovery (Prior Art; Ahir et al., 2006);

FIG. 10 shows optical microscopy confirming the variation of fibercomposition with the ratios listed as LLDPE/SEBS (sheath/core);

FIG. 11 shows SEM images of a cross section of LLDPE sheath filamentsafter the SEBS component was dissolved away using toluene from (a)sheath/core cross-section filaments and (b) 37 islands-in-sea filaments;

FIG. 12 shows a test conducted as proof of shape memory with a presentlydisclosed 60/40 SEBS/LLDPE bicomponent fiber: (A) initial length of 25mm; (B) stretched to 400% strain; (C) released fiber at 25 mm; and (D)after 2 sec in a water bath held at 72° C.;

FIG. 13 shows micrographs from scanning electron microscopy of 40/60PE/SEBS filaments at (A) an undeformed state, (B) deformed state, and(C) recovered state;

FIG. 14 shows scanning electron microscopy evidence of plasticdeformation and recovery: (A) deformed state at 400% strain (B)recovered state;

FIG. 15 shows single filament tensile testing on 25/75, 40/60, and 75/25LLDPE/SEBS fiber compositions. Optical micrographs are also shown;

FIG. 16 shows cyclic loading at constant temperature with 30/70LLDPE/SEBS filaments;

FIG. 17 shows cyclic loading at constant temperature with 50/50LLDPE/SEBS filaments;

FIG. 18 shows cyclic loading followed by heating/cooling cycles with30/70 LLDPE/SEBS filaments;

FIG. 19 shows cyclic loading followed by heating/cooling cycles with50/50 LLDPE/SEBS filaments;

FIG. 20 shows the results on adhesion when the sheath component isvaried;

FIG. 21 shows shape-memory dependence on the sheath component;

FIG. 22 shows a hypothesis of sheath/core shape memory; and

FIG. 23 shows a hypothesis of sheath/interlayer/core shape memory.

DETAILED DESCRIPTION

The presently disclosed subject matter now will be described more fullyhereinafter with reference to the accompanying Figures, in which some,but not all embodiments of the presently disclosed subject matter areshown. Like numbers refer to like elements throughout. The presentlydisclosed subject matter may be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein;rather, these embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Indeed, many modifications andother embodiments of the presently disclosed subject matter set forthherein will come to mind to one skilled in the art to which thepresently disclosed subject matter pertains having the benefit of theteachings presented in the foregoing descriptions and the associatedFigures. Therefore, it is to be understood that the presently disclosedsubject matter is not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of the appended claims.

I. Multicomponent Fibers or Films Capable of Thermally Induced ShapeRecovery after Low-Temperature Strain Fixing

The presently disclosed subject matter provides multicomponent fibers orfilms capable of thermally induced shape recovery after two types ofstrain fixing under conditions of (1) ambient temperature programming or(2) conventional heated programming Without wishing to be bound to anyone particular theory, such properties are imparted on the presentlydisclosed fibers or films by separating the two features responsible forshape memory in a polymeric material: (1) a network-forming species and(2) a species exhibiting a switching mechanism when heated. It has beenfound that the incorporated components (not necessarily two) possessstrong interfacial adhesion with at least one other component, whichallows them to function as a single mechanical structure.

When subjected to a mechanical load, the components undergo deformationin a different fashion. The network-forming component, e.g., a corecomponent, which in some embodiments is a thermoplastic elastomer (TPE),maintains a physically crosslinked network and is capable of recoveringto its undeformed state when the load is removed. The switchingcomponent, e.g., a sheath component, reorders due to plastic deformationand retains the deformed shape. The interface between the two componentsremains largely intact, which results in a temporary deformed shape ofthe fibers or film. When the deformed fibers or film are heated in sucha way that the sheath component (capable of switching) melts andsoftens, the core component (e.g., TPE) pulls it back to the originalshape as a result of its own elasticity and at least partially preservedinterfacial integrity.

A. Overview: Shape-Memory Polymers

A schematic illustrating shape-memory behavior is provided in FIG. 1.

Polymeric materials exhibiting shape recovery require a molecular orsupramolecular network that consists of long chains that define theinitial shape (Lendlein and Kelch, 2002). The networks are stabilized by“binding” or “net” points, which remain intact upon exposure to thestimulus and thus enable memory of the initial shape (Liu et al., 2007).Therefore, the net points in a SMP network define the original shape andthe chains connected by the net points impart the elasticity requiredfor the deformed network to reacquire its initial shape afterstimulation.

Shape-memory polymers also require recovery elements, or switchingsegments, in the network that are capable of forming temporaryinteractions (Liu et al., 2007; Lee et al., 2000). The interactionsbetween these switching segments are affected by the external stimulus((Lendlein and Kelch, 2002; Behl and Lendlein, 2007). The retention oftemporary shape and the transition back to the original shape from thetemporary shape are determined by the stimuli-responsive switchingsegments (Wei et al., 1998). Accordingly, the switching segmentsdetermine the transition/stimulation conditions of SMPs.

Recent advances in shape-memory materials have led to the development ofmultiple shape recoveries in an SMP network (Behl et al., 2010). Thenetworks are capable of recovering partially to a secondary temporaryshape (Bellin et al., 2006; Xie et al., 2009). Latest developments arecapable of multiple-shape memory, wherein several temporary states ofthe material can be captured en route to the final recovery of the SMPnetwork (FIG. 2; Xie, 2010). For example, triple and quadrupleshape-memory stimulated by temperature was demonstrated in Nafion (Xie,2010). Such capabilities open new avenues for SMPs in the fields ofdeployable space structures, and smart dry adhesives, as well asadaptive biomedical devices (Xie, 2010).

Shape-memory polymers can be broadly classified on the basis ofcomposition into the following four different types (Liu et al., 2007):(I) covalently cross-linked glassy thermoset networks; (II) covalentlycross-linked semi-crystalline networks; (III) physically cross-linkedglassy copolymers; and (IV) physically cross-linked semi-crystallineblock copolymers.

1. Covalently Cross-Linked Glassy Thermoset Networks (Type I).

These materials are composed of a cross-linked polymer network thatexhibits a sharp glass transition temperature (T_(g)). They behave aselastomers beyond T_(g), which can be tuned by varying the cross-linkdensity and, in the case of bi/multicomponent systems, the composition.For example, chemically cross-linked vinylidene random copolymers ofpoly(methyl methacrylate) and poly(butyl methacrylate) have T_(g)'s of110° C. and 20° C., respectively. By varying the composition of thesetwo species in the material, a sharp and tunable T_(g) can be achievedfor the resulting SMP network (Liu and Mather, 2002).

Ultra-high molecular weight glassy polymer networks can also beconsidered as this type of SMP because they do not flow above theirT_(g). These types of materials also show good shape fixity due tovitrification. Examples of such materials include high-molecular-weightpoly(methyl methacrylate) (Irie, 1998). Polystyrene copolymers, epoxynetworks and amorphous polyurethanes constitute other examples ofchemically cross-linked glassy SMPs (Tong, 2002; Beloshenko et al.,2003); Chen et al., 2002).

2. Covalently Cross-Linked Semi-Crystalline Networks (Type II).

Polymers in this category use their inherent crystallinity to establishthe conditions associated with shape fixing and memory (Liu et al.,2007). In this case, the melting temperature (T_(m)) of the polymereffectively becomes the transition temperature for the SMP network. Thepermanent shape of these networks is established similarly to that ofthe first category by chemical cross-links (Behl and Lendlein, 2007; Liuet al., 2007). Since melting is a first-order transition (unlike a glasstransition, which is second order), the shape recovery is much faster ascompared to the first case. The transition temperatures also are muchnarrower in range (Liu et al., 2007).

These SMPs include bulk polymers that form crystalline domains (Otsukaet al., 1998). Examples of materials in this category of SMPs includechemically cross-linked semi-crystalline rubber (Otsuka et al., 1998;Zhu et al., 2003) and polycaprolactone (Chowdhury and Das, 2003). Aschematic of this type of material is provided in FIG. 3. The circlesrepresent the permanent cross-links responsible for the original shapeand the chains (chains seen in Shape A) indicate crystalline domainsthat provide temporary fixation of the network. One significantdisadvantage of these materials is that crystallinity is often hinderedby the presence of the shape-restoring chemical cross-links. Thislimitation is responsible for the SMP having a broad crystal sizedistribution and, hence, a broadened transition temperature (Liu et al.,2007).

Once initially shaped, Type I and II SMPs cannot be processed again intoanother shape or form. They also present significant challenges torecycling and reuse (Otsuka and Wayman; 1998). Chemical cross-linking isintroduced by site-specific reactions that form covalent bonds betweenneighboring chains and is therefore a stochastic phenomenon that cancontinue beyond the time of the primary reaction. The result isadditional cross-linking and eventual embrittlement (Liu et al., 2007;Otsuka and Wayman, 1998). Physically cross-linked networks developed onthe basis of microphase separation or site-specific interactions (e.g.,hydrogen bonding or electrostatic interactions) possess significantadvantages over the previous materials for long-term end-useapplications (Lendlein and Kelch, 2002; Behl and Lendlein, 2007).

3. Physically Cross-Linked Glassy Copolymers (Type III).

These SMPs have unique advantages due to their rheological propertiesthat facilitate melt processing using conventional thermoplastictechnology (Liu et al., 2007; Otsuka and Wayman, 1998). This class ofmaterials is characterized by the presence of rigid, amorphousmicrodomains that serve as physical cross-links. One example of suchmaterials includes microphase-separated block copolymers (Lee et al.,2001; Ahir et al., 2006). These materials exhibit excellent recoverybeyond the transition temperature for rapid shape recovery (Otsuka andWayman, 1998; Lee et al., 2001). Another species is, however, requiredto introduce temporary shape fixation in the network through eithercrystallization or vitrification (Liu et al., 2007; Lee et al., 2001).

Examples of Type III materials include, but are not limited to,polylactide copolymers (Min et al., 2005), aromaticamide/polycaprolactone blends (Kraft and Rabani, 2004),polyamide/polycaprolactone blends (Lee et al., 2000), and polyethyleneterephthalate/polyethylene oxide blends (Luo et al., 1997). Polyurethaneblock copolymers exhibiting a sharp glass transition also belong to thiscategory. Another example is the miscible blend of a segmentedpolyurethane with phenoxy resin and polycaprolactone (Jeong et al.,2001). In addition to block copolymer systems, homopolymer blends, suchas those composed of poly(methyl methacrylate) and poly(vinylidenefluoride), can yield a melt-miscible system over all compositions (Campoand Mather, 2005). In this case, the poly(methyl methacrylate) isamorphous, while the poly(vinylidene fluoride) crystallizes to serve asthe source of physical cross-linking and likewise contributes to themodulus of the blend. The SMP transitions at the glass transition of theacrylic (Campo and Mather, 2005).

Other physical associations, such as hydrogen bonding and ionicclusters, also can serve as physical cross-links (Li et al., 1998; Kimet al., 1998). These cross-links exist in the hard segments of thenetworks and can be dissociated when melt- or solution-processing thepolymer network. Such a material is reusable and can be reshapedmultiple times.

4. Physically Cross-Linked Semi-Crystalline Block Copolymers (Type IV).

In this case, the block copolymers contain a soft segment that iscapable of crystallizing so that the melting point of this speciesestablishes the transition of the SMP network (Liu et al., 2007). Aclassic example of this type of material is apoly[styrene-b-(trans-butadiene)-b-styrene) triblock copolymer (Ikematsuet al., 1990). The styrenic endblocks constitute 10-30 wt % of themolecule, and the system develops into a strongly-segregated networkcomposed of a semi-crystalline polybutadiene matrix. Endblock-richmicelles exhibit a glass transition at 92° C. (depending on blocklength), above which the copolymer can be melt-processed. The midblock,on the other hand, melts at 68° C., thereby providing about a 30° windowfor the shape-memory functioning of the copolymer.

An entire class of thermoplastic polyurethanes (TPUs) withsemi-crystalline segments has evolved as excellent shape-memorycandidates (Li et al., 1997; Komiya et al., 1989). These TPUs can beenvisaged as multiblock copolymers with alternating hard and softsegments. The hard segments interact via hydrogen bonding, whereascrystallization of the soft segments is responsible for thetransitioning phase. Crystallization of the soft segments introduces asecondary shape in the SMP network. These materials are of considerableinterest due to their tunable stiffness and transition temperature andthey are readily foamed (Liu et al., 2007).

Shape-memory behavior in polymers can be characterized by analyzing themechanical response of the material on a stress-strain curve, asdepicted in FIG. 4. The signature response can be described in terms offour different steps as the network cycles through the loading: (1) theSMP is first heated above the transition temperature T_(trans) and aload is applied. The first step therefore corresponds to a deformationstrain ε_(m) under a given applied stress; (2) the temperature is thenlowered below T_(trans) and the temporary shape is fixed in the network;(3) the load is withdrawn from the SMP and a strain ε_(u) remains. Asmall strain may be recovered due to chain relaxation; and (4) uponheating above T_(trans) again, the material recovers its original shape.A permanent strain ε_(p) may be introduced into the system as a resultof this cycle

Two ratios are often used to describe shape memory in polymers: strainfixity and strain recovery. The Strain Fixity ratio (R_(f)) relates tothe strain fixed in the temporary shape under a set of loadingconditions (Behl and Lendlein, 2007) and is given by

${R_{f}(N)} = \frac{ɛ_{u}(N)}{ɛ_{m}}$

where N is the cycle number, and ε_(m) denotes the maximum strainapplied.

The Strain Recovery ratio (R_(r)) relates to the strain introduced inthe recovered SMP after returning to its original shape (Behl andLendlein, 2007) and is expressed as

${R_{r,{tot}}(N)} = {\frac{ɛ_{m} - {ɛ_{p}(N)}}{ɛ_{m}}.}$

Thermoplastic elastomers are capable of excellent strain fixity, as wellas strain recovery. Physically cross-linked networks, as describedhereinabove as Type III and IV, also are capable of moderately to veryhigh tensile deformation (Liu et al., 2007; Otsuka and Wayman, 1998;Kraft and Rabani, 2004; Li et al., 1997).

Thermodynamics, expressed in terms of repeat unit interactions and chainelasticity/packing, govern the self-organization of block copolymers andtheir blends with homopolymers or solvents. Some of the seminaltheoretical developments aimed at elucidating general polymer (and, morespecifically, block copolymer) phase behavior include: (1) quasichemicaldescription of the free energy of mixing (Huggins, 1941); (2) the randomphase approximation (de Gennes, 1979); and (3) the development ofmean-field theory (Leibler, 1980) and self-consistent field theory(Helfand, 1975).

Thermodynamic incompatibility in polymeric blends and copolymer systemscan be expressed by the Flory-Huggins interaction parameter (X), whichis incorporated into the free energy function to describe theinteraction of two chemically distinct repeat units. Although theoriginal definition of X is over-simplistic, it provides a valuableparameter that can be determined experimentally from several differentanalytical techniques (Huggins, 1941) or estimated using a variety oftheoretical approaches.

The random phase approximation employs X to predict the phase behavior(e.g., the spinodal decomposition condition) of complex multicomponentsystems primarily from small-angle scattering data (de Gennes, 1979). Italso can be used to measure X

Self-consistent field theory generally can be used to predict theequilibrium properties of a microphase-separated (or -ordered) blockcopolymer or a physical mixture containing a block copolymer if X andthe copolymer architecture and characteristics (block lengths andincompatibilities) are known. The premise behind this theoreticalapproach is that the repeat units comprising the blocks of the copolymerare spatially arranged in such fashion that the field they introducemust be uniform and consistent with the copolymer characteristics sothat the free energy is minimized. In the case of blockcopolymer/homopolymer blends, microphase-separated morphologies can bepredicted in this fashion, but macrophase separation cannot. Another useof this framework is to predict the equilibrium distribution of blockcopolymer molecules at an interface.

Triblock copolymers (for example, thermoplastic elastomers availablefrom Kraton) blended with polyolefins are of prime consideration forpractical and fundamental purposes. The rubbery midblock of eachcopolymer shows affinity toward polyolefins, such as polyethylene orpolypropylene, whereas the styrenic endblocks microphase-separate andform well-defined microdomains. In the case of fibers as one of thetargeted shape-memory outcomes, the size of the glassy endblocks islimited by viscosity constraints. In some of the formulations designedherein, the copolymer endblocks either self-assemble into spheroidalmicelles or, in rare cases, cylindrical (worm-like) micelles (Mark,1996). It should be noted that the high-molecular-weight polyolefinsused herein and some styrenic copolymers, e.g., Kraton® copolymers,macrophase-separate when melt-blended (Li et al., 2002).

B. Representative Embodiments

Shape-memory behavior in polymer fibers or films is principally dictatedby the relaxation of polymer molecules, as well as the phase-separatedmorphology present (if one exists). In a representative, non-limitingexample, thermoplastic elastomers (TPEs) and their blends with variouspolymers, including, for example, polyolefins, can, under favorableconditions, self-assemble into supramolecular networks that exhibitexcellent memory of shape and form. The presently disclosed subjectmatter provides, in some embodiments, multicomponent polyolefin/TPEfibers or films produced at different compositions and concentricgeometries that impart shape memory upon cyclic loading.

More particularly, in some embodiments, the presently disclosed subjectmatter introduces shape-memory properties into devices usingcommercially available polymers that are already produced on anindustrial scale. The compositions and methods of the presentlydisclosed subject matter are cost effective and, because no complexprocessing is involved, the materials are easily recyclable. Anothersignificant advantage of the presently disclosed compositions is thatthe recovery of the permanent shape in the fibers or films is broughtabout in a very short time (in some embodiments, under 2 sec) under theexternal stimulus.

In some embodiments, the presently disclosed subject matter relates tomulticomponent, for example, bicomponent, melt-spun fibers ormelt-extruded/pressed films that exhibit shape recovery properties whenheat is applied as an external stimulus. Accordingly, in someembodiments, the presently disclosed methods include mixing or blendingtwo or more polymer components to form a bicomponent fiber or film.

As used herein, the term “component” refers to a separate part of afiber or film that has a spatial relationship to another part of thefiber or film. By way of illustration, a bicomponent fiber comprises twocomponents that can be configured in, for example, a sheath-core orislands-in-the-sea configuration, wherein the sheath comprises onecomponent and the core comprises another component that can be the sameor different than that of the sheath. Further, the term “component” canrefer to a part of a fiber that imparts some structural characteristicto the fiber, e.g., a core, sheath, or other cross-sectional segment ofthe fiber, or a part of a fiber that can be selectively removed from thefiber to impart some other characteristic to the fiber, for example,porosity.

As used herein, the term “multicomponent fiber” refers to a fiber formedfrom two or more components, e.g., two or more polymeric materials, thathave been extruded from separate extruders and are then spun together toform a contiguous interface that extends along the length of the fiber.Multicomponent fibers also can be referred to art as “conjugate fibers.”The two or more components comprising a multicomponent fiber typicallyare different from each other, although multicomponent fibers also canuse the same material, e.g., the same polymeric material, for eachcomponent. Further, a multicomponent fiber also can be formed byextruding a blend or mixture of two or more components from the sameextruder and then spinning the extrudate to form a continuous fibercomprising the two or more components.

In particular embodiments, two components are used to form amulticomponent fiber and the product is referred to as a “bicomponentfiber.” A “bicomponent fiber” can be formed by combining, inheterogeneous fashion two components, e.g., two polymeric materials,having, for example, different or, in some embodiments, the samechemical and/or physical properties, and extruding the combinedmaterials together from the same spinneret. The two componentscomprising a bicomponent fiber can be present in any desired ratio, forexample, 99:1, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40,55:45, 50:50, 45:55, 40:60, 30:70, 25/75, 20:80, 15:85, 10:90, 5:95,1:99 and the like at intermediate compositions. In particularembodiments, the fiber or film has a core or island component and asheath component in a w/w ratio of about 40/60 (sheath/core). It shouldbe understood, however, that the scope of the presently disclosedsubject matter includes fibers with more than two components andpossessing various other possible cross-sectional geometries including,but not limited to, trilobal core, sheath/interlayer/core,islands-in-sea, segmented pie, and side-by-side geometries. For example,when three components, e.g., three polymeric materials, at least two ofwhich can be the same, are used to form the multicomponent fiber, theproduct is referred to as a “tricomponent fiber.”

Bicomponent fibers can be configured in various spatial arrangementswherein each component is arranged in substantially the same position indistinct segments across the cross-section and extends continuouslyalong the length of the fiber. Representative spatial arrangements ofbicomponent fibers include, but are not limited to, concentricsheath-core, eccentric sheath-core, tipped tri-lobal, and “islands inthe sea”.

As used herein, the term “sheath-core” or “sheath/core” refers to amulticomponent fiber having a core component surrounded, or enclosed, byat least one outer layer, or sheath, of a second component, and in someembodiments, e.g., in a tricomponent fiber, a third component. In suchconfigurations, the sheath can be continuous or non-continuous aroundthe core. The ratio, measured by weight or by volume, of the sheath tothe core can be from about 95/5 to about 5/95, that is, about 95/5,90/10, 85/15, 80/20, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 45/55,40/60, 35/65, 30/70, 25/75, 20/80, 15/85, 10/90, 5/95, and the like atintermediate compositions.

Sheath-core fibers can be concentric, wherein the core component iscentered relative to the sheath component, or eccentric, wherein thecore is shifted off-center. Further, sheath-core fibers can have variousouter geometries, i.e., a geometry defined by that of the sheath,including, but not limited to, substantially round or circular, oval,elliptical, star-shaped, rectangular, and other eccentricities. The corefilament also can have various geometries, including circular ormulti-lobal, for example tri-lobal. Further, the core in sheath-corefibers can be hollow or non-hollow, e.g., solid, or have a porous, solidcore. Multiple cores can be simultaneously generated in the “islands inthe sea” geometry.

Representative materials for use in elastomeric bicomponent fibers aredisclosed in U.S. Patent Application Publication No. 2007/0055015 A1 toFlood et al., entitled “Elastomeric Fibers Comprising ControlledDistribution Block Copolymers,” published Mar. 8, 2007; U.S. Pat. No.7,662,323 B1 to Flood et al., entitled “Elastomeric Bicomponent FibersComprising Block Copolymers Having High Flow,” issued Feb. 16, 2010;U.S. Pat. No. 7,910,208 B2 to Flood et al., entitled “ElastomericBicomponent Fibers Comprising Block Copolymers Having High Flow,” issuedMar. 22, 2011; and U.S. Pat. No. 8,003,209 B2 to Flood et al., entitled“Elastomeric Bicomponent Fibers Comprising Block Copolymers Having HighFlow,” issued Aug. 23, 2011, each of which is incorporated herein byreference in its entirety.

More particularly, in some embodiments, the presently disclosed subjectmatter provides a multicomponent melt-spun fiber that exhibitsdeformation at room temperature, as well as at temperatures beyond thesoftening temperature of the switching component (but below thedisruption of the molecular network), and shape recovery properties whenheat is applied. In some embodiments, the fiber is a bicomponent fiberthat comprises two co-spun or co-extruded components in a core-sheathcross-sectional geometry, wherein the core component is a multiblockcopolymer and the sheath component comprises a second component that isdifferent from the core component, and the fiber can be deformed at roomtemperature conditions and recover its shape when heated. In otherembodiments, islands-in-the-sea filaments comprised of a multiblockcopolymer in the islands and the homopolymer as the sea componentexhibit shape recovery when a temporary deformation is induced byambient-temperature or heated programming.

As used herein, the term “multiblock copolymer” refers to any blockcopolymer possessing more than two chemically dissimilar contiguoussequences (“blocks”) arranged in either linear or non-linear fashion.Multiblock copolymers possessing glassy/crystalline and rubbery blocksthat microphase-separate to form a physically crosslinked rubberynetwork are commonly referred to as thermoplastic elastomers (TPEs).

The presently disclosed filaments can be deformed by loading at roomtemperature conditions. Recovery to the original shape is nearlyspontaneous (for example, within 2 sec of heating or within about 5 secafter being exposed to a thermal stimulus) and is almost complete. Thepresently disclosed multicomponent fibers exhibit repeatable shaperecovery and are capable of deformations above 400% strain (e.g., atleast about four times the original length). Similar strain fixity andrecovery behavior are observable under heated programming conditions.

The presently disclosed fibers can be multicomponent fibers and, in someembodiments, are bicomponent fibers or tricomponent fibers. Inparticular embodiments, the fibers are bicomponent fibers. Generally,the presently disclosed multicomponent fibers, e.g., in someembodiments, a bicomponent fiber, comprise at least one component, e.g.,a core component, capable of forming a physically crosslinked networkand another component, e.g., a sheath component, capable oftransitioning with thermal stimulus, wherein the two components havestrong interfacial adhesion; and wherein the temperature associated withthe transitioning component is lower than the temperature required todisrupt the molecular network of the other component.

In some embodiments, the core can be an elastic material, such as athermoplastic elastomer as described herein below. In certainembodiments, the core has an upper T_(g) between about 95° C. and about100° C., although this T_(g) can be tuned through the inclusion ofadditives in the material comprising the core. Accordingly, in someembodiments, the transition point of the core material is higher than100° C. and, in some embodiments, can be as high as 140° C. (Martins etal., 2003). Therefore, in some embodiments, the core component furthercomprises one or more additives and has an upper glass transitiontemperature in the range from about 90° C. to about 140° C. In someembodiments, the additive comprises a long-chain alkyl compound. In someembodiments, the upper glass transition temperature can be increasedeven more through modification.

The sheath functions as the switching point in the presently disclosedshape-memory fibers and, in some embodiments, the sheath comprises apolyolefin as described herein below. Generally, the material comprisingthe sheath has a melting point lower than the upper T_(g) of thematerial comprising the core. For example, in representative,non-limiting embodiments, the material comprising the sheath has amelting point lower than about 95° C.

More particularly, in some embodiments, the core comprises athermoplastic elastomer (TPE). Thermoplastic elastomers generally are aclass of copolymers that have both thermoplastic and elastomericproperties and exhibit the advantages typical of elastomers andplastics. Physical crosslinking contributes to the highly elasticproperties exhibited by thermoplastic elastomers. Elastomers can bephysically cross-linked (thermoplastic elastomers) or chemicallycross-linked (permanent elastomers). Thermoplastic elastomers typicallyhave the following characteristics: the ability to be stretched tomoderate elongations and, upon removal of the stress, return toapproximately its original shape; processable as a melt at elevatedtemperatures; and absence of significant creep.

Commercially available TPEs include at least seven general classes:styrenic block copolymers; acrylic block copolymers; polyolefin blends,such as ethylene propylene diene (EPDM)/polypropylene (PP) andnitrile-butadiene rubber (NBR)/PP; elastomeric alloys, such as athermoplastic vulcanate, e.g., TPE-v or TPV;

thermoplastic polyurethanes (TPU), including polyether and polyesterurethanes; thermoplastic copolyesters; and thermoplastic polyamides.Representative commercially available block copolymer TPEs include, butare not limited to, ARNITEL® (DSM Engineering Plastics, Birmingham,Mich., United States of America), a copolyester; ENGAGE™ (Dow Chemical,Midland, Mich., United States of America), a polyolefin; HYTREL®(DuPont, Wilmington, Del., United States of America), a polyester;DRYFLEX® and MEDIPRENE® (Elasto, Sweden), SEBS-based materials; andKRATON® styrenic block copolymers (Kraton Performance Polymers, Houston,Tex., United States of America); and SEPTON® styrenic block copolymers(Kuraray America, Houston, Tex., United States of America).

In particular embodiments, the core comprises a styrenic blockcopolymer, including, but not limited topoly(styrene-b-butadiene-b-styrene) (SBS),poly(styrene-b-isoprene-b-styrene) (SIS),poly[styrene-b-(ethylene-co-propylene)-b-styrene] (SEPS), orpoly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS). In particularembodiments, the core comprises SEBS. In particular embodiments, thecore component comprises SEBS.

In some embodiments, the sheath comprises a polyolefin. Polyolefinsgenerally are polymers produced from a simple olefin, i.e., an alkene,having the general formula C_(n)H_(2n) as a monomer. For example,polyethylene is produced by polymerizing ethylene, polypropylene isproduced by polymerizing propylene, and the like. Representativepolyolefins suitable for use with the presently disclosed subject matterinclude thermoplastic polyolefins including, but not limited to,polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), andpolybutene-1 (PB-1). In particular embodiments, the sheath compriseslinear low density polyethylene (LLDPE). LLDPE is a substantially linearpolymer commonly made by copolymerization of ethylene with longer-chainolefins. LLDPEs differ structurally from conventional low-densitypolyethylene (LDPE) because of the absence of long chain branching.LLDPE has a higher tensile strength than LDPE and is very flexible andelongates under stress.

In further embodiments, the presently disclosed subject matter providestricomponent fibers. In some embodiments, the presently disclosedtricomponent fiber comprises three co-spun or co-extruded componentsconfigured in an inner core component-outer core component-sheathcomponent cross-sectional geometry, wherein at least one of the corecomponents comprises a thermoplastic elastomer and the sheath componentcomprises a polyolefin, and wherein the fiber can be deformed from anoriginal shape and return to the original shape in response to a thermalstimulus, e.g., when heated. In particular embodiments, the inner corecomponent/outer core component/sheath component compriseLLDPE/SEBS/LLDPE.

Extrusion processes for making multicomponent continuous fibers andfilms are known in the art and are not described in detail herein.Generally, to form a multicomponent fiber, two or more components, forexample, two or more polymeric materials which can be the same ordifferent, are extruded separately and fed into a polymer distributionsystem, wherein the components are introduced into a spinneret havingone or more capillaries. In such embodiments, the two components arecombined in a common capillary. Alternatively, a single extrudatecomprising a blend or mixture of two or more components can be extrudedand introduced into the spinneret. The spinneret can be configured suchthat the extruded fiber has the desired cross section, for example,sheath-core or tipped tri-lobal. Such a process is described, forexample, in U.S. Pat. No. 5,162,074 to Hills, which is incorporatedherein by reference in its entirety.

In particular embodiments, the presently disclosed multicomponent fiberscan be produced by co-extruding two components in a core-sheath,islands-in-sea, side by side, or other bicomponent cross-sectionalgeometry through a melt-spinning process. Although a variety of ways toproduce multicomponent fibers exist, including wet spinning and dryspinning, producing a multicomponent fiber through melt spinning canoffer several advantages. Melt-spun multicomponent fibers generally areresistant to higher temperatures and chemicals and can be several timesstronger than multicomponent fibers produced by other methods. Melt-spunfibers also can be advantageous for use in structures, such as thoseused in blood treatment procedures, because the surface roughness of thefiber walls can be smaller than that of wet spun fibers. See de Rovere,A. and Shambaugh, R. L., “Melt-spun hollow fibers for use in nonwovenstructures.” Ind. Eng. Chem. Res., 40:176-187 (2001).

The individual components of the multicomponent fiber can be selected tohave melting temperatures such that the components can be extruded andspun through a common capillary at about the same temperature withoutdegrading one component or the other. The processing temperature isdetermined by the chemical nature, molecular weights and concentrationof each component. The extrusion and spinning process typically occursat a melt temperature between about 90° C. to about 350° C., forexample, in some embodiments about 175° C., depending on the meltproperties of the two components.

The presently disclosed subject matter pertains not only to fibers, butalso to films comprising at least two co-spun or co-extruded componentsconfigured in a core component-sheath component cross-sectionalgeometry. The film can be a hollow tube, relatively flat, or othersuitable structure. As such, the presently disclosed subject matterprovides a multicomponent film comprising at least two co-spun orco-extruded components configured in a core component-sheath componentcross-sectional geometry, wherein the core component comprises athermoplastic elastomer and the sheath component comprises a polyolefin,and wherein the film can be deformed from an original shape and returnto the original shape when heated. In particular embodiments, the corecomponent comprises SEBS and the sheath comprises LLDPE. In arepresentative, non-limiting example, the film includes a bilayer filmcomprising LLDPE/SEBS (sheath layer/core layer). As another example, thefilm is a trilayer film comprising LLDPE/SEBS/LLDPE (sheath layer/outercore layer/inner core layer).

As used herein the term “blend” and derivatives thereof refers to amacroscopic mixture of two or more different polymers, whereas the term“mixture” and derivatives thereof can refer to either a homogeneous orheterogeneous combination of two or more different polymers. The term“admixing” and derivatives thereof is intended to encompass both“blending” and “mixing” of a combination of components. Such blends canbe extruded and subsequently spun into fibers. The spinning can befollowed by hot drawing at a constant draw ratio to form bicomponentfibers. The resulting fibers can be washed in a shaker bath, sonicatedin an ultrasonicator for a period of time, and then vacuum dried.

Unless otherwise indicated, the term “fiber” as used herein refers tofibers having a substantially continuous structure, such as continuousfilaments, and fibers of finite length, such as conventional staplefibers. The term “staple fiber” refers to a non-continuous fiber, whichcan be produced with a conventional fiber spinning process and then cutto a staple length, from about one inch to about eight inches.

Further, as used herein, a “substantially continuous filament of fibers”refers to filaments or fibers prepared by extrusion from a spinneret,which are not cut from their original length. Substantially continuousfilaments or fibers can have average lengths ranging from greater thanabout 15 cm to more than one meter. Spunbond fibers typically havediameters larger than about 5 microns, frequently, between about 10 and20 microns. Spunbonding methods are described, for example, in U.S. Pat.No. 4,340,563 to Appel et al., U.S. Pat. No. 3,692,618 to Dorschner etal., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. No. 3,338,992and U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 toHartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No.3,542,615 to Dobo et al., each of which is incorporated herein byreference in its entirety.

C. Applications

In general, the presently disclosed multicomponent fibers can be used toform a variety of articles. These articles include elastic monofilaments, woven fabrics, spun bond non-woven fabrics or filters,melt-blown fabrics, staple fibers, yarns, bonded, carded webs, and thelike. Any of the processes typically used to make these articles can beemployed when they are equipped, for example, to extrude two materialsinto a bicomponent fiber.

In particular, non-woven fabrics or webs can be formed by any of theprocesses known in the art. One process, typically referred to asspunbond, is well known in the art. U.S. Pat. No. 4,405,297, which isincorporated herein by reference in its entirety, describes a typicalspunbond process. The spunbond process commonly comprises extruding thefibers from the melt through a spinneret, quenching and/or drawing thefibers using an air flow, and collecting and bonding the non-woven web.The bonding of the non-woven web is typically accomplished by anythermal, chemical or mechanical methods, including water entanglementand needle punch processes, effective in creating a multiplicity ofintermediate bonds among the fibers of the web. Non-woven webs also canbe formed using melt-blown process such as described in U.S. Pat. No.5,290,626, which is incorporated herein by reference in its entirety.Carded webs may be formed from non-woven webs by folding and bonding thenon-woven web upon itself in the cross machine direction.

Non-woven fabrics comprising the presently disclosed multicomponentfibers can be used for a variety of elastic fabrics including, but notlimited to, diapers, waist bands, stretch panels, disposable garments,medical and personal hygiene articles, filters, and the like.

Elastic mono-filaments of the presently disclosed multicomponent fiberscan be continuous, single, bicomponent fibers used for a variety ofpurposes and can be formed by any of the known methods of the artcomprising spinning, drawing, quenching and winding. As used herein,staple fiber means cut or chopped segments of the continuouslycoextruded bicomponent fiber.

Yarns of the presently disclosed multicomponent fibers can be formed byprocesses known in the art. U.S. Pat. No. 6,113,825, which isincorporated herein by reference in its entirety, teaches the generalprocess of yarn formation. In general, the process comprises meltextrusion of multiple fibers from a spinneret, drawing and winding thefilaments together to form a multi-filament yarn, extending orstretching the yarn optionally through one or more thermal treatmentzones, and cooling and winding the yarn.

The articles comprising the presently disclosed multicomponent fiberscan be used alone or in combination with other articles made with thebicomponent fibers or with other classes of materials. As an example,non-woven webs can be combined with elastic mono-filaments to provideelastic stretch panels. As another example, non-woven webs can be bondedto other non-elastomeric non-woven webs or polymeric films of manytypes.

More particularly, an emerging class of materials, SMPs can be used in awide variety of applications ranging from in vivo implants to outerspace applications. Their low densities and large allowable deformationsmake them suitable for deployable components in aerospace (Metcalfe etal., 2003). These applications include hinges, trusses, antennas,optical reflectors, and morphing skins.

One type of application for SMPs is in the biomedical field. Since thediscovery of SMPs in the 1980s, biocompatible polymers and their blendswere consistently developed to enhance stimuli responsive behavior(Hampikian et al., 2006). One pioneering application for SMP smartmaterials is controlled drug release (Feninat et al., 2002). Inaddition, polymer vascular stents have been developed that also serve asdrug delivery devices (Wache et al., 2003). FIG. 5 depicts yet anotherimportant biomedical application of the SMP materials as wound closuresutures.

Another type of application for SMPs is in deployable structures.Devices fabricated using SMPs and their variants have overcome someinherent disadvantages over conventional devices. These disadvantagesinclude complex assembling process, massive mechanisms, large volumes,undesired deployment defects, and high densities. One application is toreplace hinges in deployable devices. A carbon-fiber-reinforced SMPcomposite was investigated (Lan et al., 2009) with flexural deformationas the main mode of deformation.

Actuation of solar arrays using the SMP component also has beendemonstrated by Leng and coworkers (Lan et al., 2009; FIG. 6). Thecomposite hinge consists of two curved cylindrical SMP shells, as shownin FIG. 6B. Voltages on the order of 20V are applied to the embeddedheating resistors in each cylindrical SMP shell. Complete actuation isachieved within 100 seconds of heating, as shown in FIG. 7.

In particular embodiment, the presently disclosed fibers can be used inthermal actuation applications, including, but not limited to, formfitting materials, packaging with self-sealing capability, deployabledevices, smart textiles, intelligent fibers, and the like.

III. Definitions

Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation. Unlessotherwise defined, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which this presently described subject matter belongs.

By “programming”, it is meant mechanical deformation and subsequentfixation of the deformation.

By ‘recovery’, it is meant an external stimulus causing a polymer toswitch from a temporary shape back to its initial shape.

The term “returning to the original shape” or “return to the originalshape” refers to the fiber or film reforming to its original shape afterheating. In some embodiments, the fiber or film returns to at leastapproximately 70% of its original shape. In other embodiments, the fiberor film returns to approximately 90% or more of its original shape, suchas 95%, 96%, or 97% of its original shape.

The term “room temperature” in non-limiting embodiments refers totemperatures from about 18° C. to about 30° C., e.g., 18, 19, 20, 21,22, 23, 24, 25, 26, 27, 28, 29, or 30° C. In some embodiments, the termroom temperature refers to a temperature of about 20° C. In otherembodiments, the term room temperature refers to a temperature of about25° C.

As used herein the term “monomer” refers to a molecule that can undergopolymerization, thereby contributing constitutional units to theessential structure of a macromolecule or polymer.

A “polymer” is a molecule of high relative molecule mass, the structureof which essentially comprises the multiple repetition of a unit derivedfrom molecules of low relative molecular mass, i.e., a monomer.

Following long-standing patent law convention, the terms “a,” “an,” and“the” refer to “one or more” when used in this application, includingthe claims. Thus, for example, reference to “a subject” includes aplurality of subjects, unless the context clearly is to the contrary(e.g., a plurality of subjects), and so forth.

Throughout this specification and the claims, the terms “comprise,”“comprises,” and “comprising” are used in a non-exclusive sense, exceptwhere the context requires otherwise. Likewise, the term “include” andits grammatical variants are intended to be non-limiting, such thatrecitation of items in a list is not to the exclusion of other likeitems that can be substituted or added to the listed items.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing amounts, sizes, dimensions,proportions, shapes, formulations, parameters, percentages, parameters,quantities, characteristics, and other numerical values used in thespecification and claims, are to be understood as being modified in allinstances by the term “about” even though the term “about” may notexpressly appear with the value, amount or range. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are not and need not beexact, but may be approximate and/or larger or smaller as desired,reflecting tolerances, conversion factors, rounding off, measurementerror and the like, and other factors known to those of skill in the artdepending on the desired properties sought to be obtained by thepresently disclosed subject matter. For example, the term “about,” whenreferring to a value can be meant to encompass variations of, in someembodiments, ±100% in some embodiments ±50%, in some embodiments ±20%,in some embodiments ±10%, in some embodiments ±5%, in some embodiments±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from thespecified amount, as such variations are appropriate to perform thedisclosed methods or employ the disclosed compositions.

Further, the term “about” when used in connection with one or morenumbers or numerical ranges, should be understood to refer to all suchnumbers, including all numbers in a range and modifies that range byextending the boundaries above and below the numerical values set forth.The recitation of numerical ranges by endpoints includes all numbers,e.g., whole integers, including fractions thereof, subsumed within thatrange (for example, the recitation of 1 to 5 includes 1, 2, 3, 4, and 5,as well as fractions thereof, e.g., 1.5, 2.25, 3.75, 4.1, and the like)and any range within that range.

EXAMPLES

The following Examples have been included to provide guidance to one ofordinary skill in the art for practicing representative embodiments ofthe presently disclosed subject matter. In light of the presentdisclosure and the general level of skill in the art, those of skill canappreciate that the following Examples are intended to be exemplary onlyand that numerous changes, modifications, and alterations can beemployed without departing from the scope of the presently disclosedsubject matter. The synthetic descriptions and specific examples thatfollow are only intended for the purposes of illustration, and are notto be construed as limiting in any manner to make compounds of thedisclosure by other methods.

Example 1 Multicomponent Fibers Comprising SEBS and LLDPE

Morphological development in copolymer/homopolymer blends has beenpreviously characterized by electron microscopy and small-anglescattering. FIG. 8 shows several transmission electron microscopy (TEM)images of a molecularly symmetric ABA triblock copolymer swollen with amidblock-selective species to yield three different morphologies. Inthis case, one of the blocks is selectively stained with a heavy metaland appears dark in the image.

Tensile testing of bi/tricomponent fibers composed of a TPE/polyolefinwill yield a signature of their mechanical response to deformation.Tensile testing under cyclic loading is required to discern the level ofhysteresis of the network. Whereas the recovery can be analyzed byperforming tensile tests under different temperature conditions (Ji etal., 2006; Meng and Hu, 2008). FIG. 9 illustrates the recovery of ashape-memory fiber over two consecutive extensional cycles.

Fibers comprising poly[styrene-b-(ethylene-co-butylene)-b-styrene](SEBS) and LLDPE were spun using the co-extruder melt-spinning facility(Hills Inc.) in a concentric core-sheath geometry. Kraton G1643 was usedas the triblock copolymer and EXACT 0230 were used as the sheathmaterial. Various ratios of the two components were spun ranging from25/75 w/w SEBS/LLDPE to 75/25 SEBS/LLDPE.

Cross-sectional optical micrographs obtained from six differentcomposition ratios (see labels) are provided in FIG. 10. The fiberdiameter was relatively uniform within each composition and a cleardistinction between core and sheath existed. These images also indicatedthat the SEBS-rich fibers were physically larger in diameter. Althoughthe spinning conditions strongly impacted fiber diameter and throughput,an optimum flow rate ensured uniform fiber diameter.

The fibers shown in FIG. 10 were spun at 220° C. and a flow rate of 30m/min. The fibers were taken up onto a winder and wound without drawing.Subsequent stretching of fibers results in permanent deformation whereinthe fibers become “fluffy” and rubbery when strained beyond 100%. Thefibers do not recover the strain completely at ambient temperature.

FIG. 11 shows SEM images of a cross section of LLDPE sheath filamentsafter the SEBS component was dissolved away using toluene from (a)sheath/core cross-section filaments and (b) 37 islands-in-sea filaments.

Example 2 Single Fiber Shape Memory

The fiber samples from the preliminary spinning experiments providedimmediately hereinabove were tested for shape-memory behavior underthermally-induced recovery. In these experiments, a single fiber wasclamped to a simple Vernier caliper with a gauge length of 25 mm. Thefiber was strained up to 400% at ambient temperature, the strain wasmaintained for a predetermined time, the fiber was released at aconstant rate to the initial length, the fiber was immersed in a waterbath at 72° C. for two seconds, and the fiber recovery was measured.This procedure was repeated several times to evaluate fiber recovery.

The strain introduced to the fibers was gradually increased from 100% to400%. An irrecoverable strain at ambient temperature was observed at100% strain. The fibers exhibited excellent shape recovery within asecond of immersion in a water bath held at 72° C. FIG. 12 illustratesthe presently disclosed procedure with the four steps in each cycle.

These fibers were shown to exhibit excellent strain recovery with a veryquick response to a thermal stimulus. The fibers also exhibitedremarkable deformation tolerance and near perfect recovery. Thisrecovery was observed even after 10 strain cycles. The fixity of thefiber was likewise being evaluated. In addition, FIG. 12C shows that thefibers had very good strain fixity, although stretching alone to 400%strain does not induce full fixity. In this experiment, the fibersneeded to be held at the desired strain for a period of time tostabilize the strain. Without wishing to be bound to any one particulartheory, it is believed that heating the spun fibers allowed thepolyolefin to flow, while the elastomer recovered the induced strain.

Example 3 Single Fiber Shape Memory

Bicomponent fibers were melt-spun in a coaxial geometry for differenthomopolymer sheaths and a thermoplastic elastomer (KRATON® G1643). Inaddition to LLDPE (EXACT® 0230), PP (BRASKEM CP360H) and PBT (CrastinS600F40NC010) also were spun as the sheath component to vary thecore-sheath interfacial adhesion. A range of fibers from 25/75sheath/core to 75/25 sheath core compositions were spun with each sheathcomponent.

Without wishing to be bound to any one particular theory, it can beassumed that the ethylene-co-butylene block of the core was thecomponent interacting with the sheath. The X values for eachhomopolymer/ethylene butylene were estimated from theoreticalthermodynamic compatibility calculations (Huggins, 1941). Details of thesolubility parameters and the X value are provided in Table 1.

TABLE 1 Theoretical estimates of the X values between EB block andHomopolymers δ_(polymer) δ_(EB) X_(EB/Polymer) (Mark, 1996) (Mark, 1996)(Huggins, 1941; Sheath component (MPa)^(1/2) (MPa)^(1/2) Mark, 1996)LLDPE 17.52 16.85 2.9 × 10⁻⁴ PP 16.40 16.85 0.5 × 10⁻⁴ PBT 24.60 16.8515.4 × 10⁻⁴ 

From the above estimate, PP is expected to have the greatest interfacialadhesion and PBT is expected to have the least adhesion. The singlefiber extension and shape-memory characteristics reveal, however, thatLLDPE has the best interfacial adhesion among the three homopolymers.

To estimate the shape-memory behavior, all fiber samples from thespinning runs were tested for shape-memory behavior underthermally-induced recovery. A single fiber was clamped to a simpleVernier caliper with a gauge length of 25 mm. The fiber was strained upto 400% at ambient temperature, the strain was maintained for apredetermined time, the fiber was released at a constant rate to theinitial length, the fiber was immersed in a water bath at 72° C. for 2seconds, and the fiber recovery was measured. This procedure wasrepeated several times to evaluate fiber recovery.

The strain introduced to the fibers was gradually increased from 100% to400%. An irrecoverable strain at ambient temperature was observed at100% strain. The fibers exhibited excellent shape recovery within asecond of immersion in a water bath held at an elevated temperaturebelow 100° C.

The LLDPE/SEBS fibers exhibit excellent strain recovery with a veryquick response to a thermal stimulus at all tested compositions. Thefibers also exhibit remarkable deformation tolerance and near perfectrecovery. This recovery was observed even after 10 strain cycles.

The PP/SEBS fibers were observed to ‘slip’ at the interface when astrain was introduced. Above 65% SEBS content, however, the PP/SEBSfibers exhibited very good strain recovery. When tested for repetitivestraining, the PP/SEBS fibers did not recover the strain completelyafter 10 cycles.

In the case of PBT/SEBS fibers, no recovery was observed at anycomposition and an interfacial ‘slipping’ was observed when strainingthe fibers. Without wishing to be bound to any one particular theory,this effect indicates that the interface between the PBT/SEBS exhibitsthe least adhesion among the tested samples. A summary of the shaperecovery observations is provided in Table 2.

TABLE 2 Shape recovery properties of the fibers under investigationSheath Adhesion Shape Composition Extent of component with core recoverydependence recovery LLDPE Very good Observed All Above 90% compositionsand repetitive PP Moderate Observed Above 65% Below 80% core and notrepetitive PBT Poor Not observed None recover No recovery

In addition, bicomponent fibers were melt-spun in a coaxial geometry fordifferent homopolymer sheaths and a core comprised of a thermoplasticelastomer (KRATON® G1643). In addition to LLDPE (EXACT® 0230), PP(BRASKEM CP360H) and PBT (Crastin S600F40NC010) also were spun as thesheath component to vary the core-sheath interfacial adhesion. Thefibers were subjected to optical and electron microscopy analysis todiscern their geometry and morphology. Shape-memory behavior of thebicomponent fibers was investigated as a function of the sheath/corecomposition for the three different homopolymer sheath components. Therecovery behavior of these fibers was verified by successive heating andstretching. Elastic modulus and storage modulus of PE/SEBS fibersincreased with an increase in the sheath (PE) content. Strain requiredto retain initial storage modulus decreased with increase in the sheath(PE) content. PE/SEBS fibers possessed excellent shape recovery in allcompositions whereas PP/SEBS fibers exhibited recovery above 65% corecomposition. Although, shape memory under cold fixity was observed inthe fibers with LLDPE and PP, PBT/SEBS fibers did not exhibit shaperecovery in any composition. PE and LLDPE are used interchangeablyherein and both refer to LLDPE.

Example 4 Shape-Memory Behavior of PE/SEBS Filaments UnderThermally-Induced Recovery

The fiber samples comprised of 40/60 PE/SEBS filaments were tested forshape-memory behavior under thermally-induced recovery. As describedabove, a single fiber was clamped to a simple Vernier caliper with agauge length of 25 mm. The fiber was strained up to 400% at ambienttemperature, the strain was maintained for a predetermined time, thefiber was released at a constant rate to the initial length, the fiberwas immersed in a water bath at 72° C. for 2 seconds, and the fiberrecovery was measured. This procedure was repeated several times toevaluate fiber recovery.

Scanning electron microscopy (SEM) of the 40/60 PE/SEBS fibers wasperformed at an undeformed state, deformed state (400% strain), andrecovered state (FIG. 13). Results showed that the filaments werecapable of very high temporary strains. The deformed filaments hadhelical grooves about 45° to the fiber axis and recovered to above 92%of their initial diameter. FIG. 14 shows the SEM evidence of plasticdeformation and recovery. Shear banding can be seen in the deformedstate at 400% strain (Panel A, FIG. 14) and is not seen in the recoveredstate (Panel B, FIG. 14).

Single filament tensile testing also was performed on the PE/SEBS fibers(FIG. 15). The quasi-static stress-strain curves were from 25/75, 40/60,and 75/25 LLDPE/SEBS fiber compositions. A gauge length of 25 mm wasused for the tensile measurements. The 75/25 LLDPE/SEBS fiber exhibitedthe largest modulus in the quasi-static testing mode among the fiberstested. Also shown in this figure are cross-sectional opticalmicrographs obtained from the different composition ratios. It wasobserved that the fiber diameter was relatively uniform within eachcomposition and there was a clear distinction between core and sheath.

A summary of tensile testing with the PE sheath/SEBS fibers is shown inTable 3. As can be seen, the storage modulus and quasi-static modulusdecreased with decreasing sheath content. In addition, the strainrequired to retain the initial storage modulus increased as sheathcontent decreased.

TABLE 3 Summary of tensile testing with the PE sheath CompositionInitial Storage Strain to Sheath/Core Modulus (MPa) Retention 75/25292 + 20 96% 40/60 145 + 12 125% 25/75 95 + 9 160%

Example 5 Cyclic Loading and Unloading

Cyclic loading studies were performed on LLDPE/SEBS sheath/core filamentbundles. A 3 mm gage length was used under a constant rate of strain.The cyclic loading and unloading was performed at a constant temperatureto determine the effect of the hysteresis of the filaments usingstress-strain behavior. Cyclic loading also was followed byheating/cooling cycles to determine the temperatures required forrecovery and the shape-memory of the filaments.

For cyclic loading at constant temperature, the loading was performed atroom temperature (25° C.). The loading was initiated with a gage lengthof 3 mm, the load was increased at a constant strain rate of 0.02 s⁻¹,and the loading was stopped at the prescribed strain (6 mm at 100% or 21mm for 600% strain). The load was then reduced until the stress reached0 MPa. The fibers were allowed to return to 0% strain or to the initialgage length (3 mm) The above steps were repeated for successive cycles.

FIG. 16 shows cyclic loading at constant temperature with 30/70LLDPE/SEBS filaments up to a 600% strain. After the first cycle, thefilaments were in a semi-crystalline state and after two cycles, thefilaments were in a rubbery state. A similar trend was seen with 50/50LLDPE/SEBS filaments at a 200% strain (FIG. 17).

For cyclic loading followed by heating/cooling cycles, the loading wasinitiated with a gage length of 3 mm, the load was increased at aconstant strain rate of 0.02 s⁻¹, and the loading was stopped at theprescribed strain. The load was then reduced until the stress reached 0MPa. The fibers were allowed to return to 0% strain or to the initialgage length (3 mm) Then the sample was heated from 25 to 75° C. at 20°C./min and cooled from 75 to 25° C./min. The above steps were repeatedfor successive cycles.

Cyclic loading followed by heating/cooling cycles was performed with30/70 LLDPE/SEBS filaments (FIG. 18). The cyclic loading and unloadingat room temperature is denoted in black lines and the response after theheating/cooling cycle is indicated by the red curves. A remarkablestrain recovery was measured and there was a rubbery response afterthermal recovery.

Cyclic loading followed by heating/cooling cycles also was performedwith 50/50 LLDPE/SEBS filaments (FIG. 19). The cyclic loading andunloading at room temperature is denoted in black lines and the responseafter the heating/cooling cycle is indicated by the red curves. Again, aremarkable strain recovery was measured. It was found that plasticdeformation dictated fixity.

Table 4 shows the shape fixity (S_(f); unrecovered temporarystrain/maximum strain) and strain recovery (S_(r); recovered strain(after heating)/maximum strain) for pure PE filaments and 50/50 and30/70 LLDPE/SEBS sheath/core bicomponent filaments.

TABLE 4 Shape Fixity and Recovery for Pure LLDPE and Bicomponent FibersSheath/Core Strain Fixity (%) Strain Recovery (%) 50/50 32.5 99.0 30/7025.0 98.3

Example 6 Shape-Memory Dependence on the Interface

The interface between the core and the sheath of a filament was examinedby varying the sheath component. In FIG. 20, experiments are shown inwhich the core of the filament was SEBS and the sheath was LLDPE, PP, orPBT. It was found that a filament with LLDPE as the sheath resulted invery good adhesion, PP resulted in good adhesion, and PBT resulted inpoor adhesion. These results, as well as other characteristics offilaments with the various sheath components, are shown in FIG. 21. Inthese experiments, LLDPE appeared to be the best sheath component interms of shape-memory characteristics. Without wishing to be bound toany one particular theory, it can be assumed that only the midblock ofthe core is in contact with the sheath component.

Shape memory in a polymer network reflects the existence of netpointsand switching segments that can be immobilized. Thermoplastic elastomersare capable of shape memory and tend to exhibit better strain recoveryas compared to chemically cross-linked networks. Bicomponent fibersproduced from a triblock copolymer and polyolefin result in increasedpolyolefin orientation under high irrecoverable strain. Single fibertesting with superimposed semi-static and oscillatory modes givesinsight on the load sharing between the constituents.

The presently disclosed subject matter can be used to develop novelmelt-spun bi/tricomponent fibers capable of shape memory by exploitingthe elasticity afforded by triblock copolymer supramolecular networks.

Example 7 Hypothesis of Shape Memory

FIG. 22 shows a hypothesis of sheath/core shape memory. In thisrepresentative embodiment, when sheath/core filaments comprisingpolyolefin/TPE are stretched, unbalanced stresses in the core and thesheath cause the filaments to coil up and crimp. This behavior decreasesthe S_(r) (strain fixity) ratio of the shape-memory fibers.

In contrast, a multicomponent fiber, such as a tricomponent fiber,exhibits enhanced shape memory. In this embodiment, the inner core andthe outer core contribute equally to the load bearing, hence abating thecrimping of filaments. The strain fixity (S_(r)) ratios for these fibersare enhanced. The sheath/interlayer/core filaments have equal stress inthe inner most and outermost components because they are the samematerial. The strain fixity and strain recovery of thesheath/interlayer/core filaments are significantly enhanced due to thebalancing of stresses on both interfaces of the TPE segment. Thisbalancing of stresses eliminates the crimping of filaments when the loadis released. As an example, the multicomponent fiber can beLLDPE/SEBS/LLDPE (sheath/outer core/inner core) as shown in FIG. 23.

REFERENCES

All publications, patent applications, patents, and other referencesmentioned in the specification are indicative of the level of thoseskilled in the art to which the presently disclosed subject matterpertains. All publications, patent applications, patents, and otherreferences are herein incorporated by reference to the same extent as ifeach individual publication, patent application, patent, and otherreference was specifically and individually indicated to be incorporatedby reference. It will be understood that, although a number of patentapplications, patents, and other references are referred to herein, suchreference does not constitute an admission that any of these documentsforms part of the common general knowledge in the art.

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Although the foregoing subject matter has been described in some detailby way of illustration and example for purposes of clarity ofunderstanding, it will be understood by those skilled in the art thatcertain changes and modifications can be practiced within the scope ofthe appended claims.

1. A multicomponent fiber or film comprising at least one componentcapable of forming a physically-crosslinked network and at least asecond component capable of transitioning in response to a thermalstimulus, wherein the two components have strong interfacial adhesion;and wherein a temperature associated with the second component capableof transitioning in response to a thermal stimulus is lower than atemperature required to disrupt the molecular network of the componentcapable of forming a physically-crosslinked network.
 2. The fiber orfilm of claim 1, wherein the fiber or film comprises at least twoco-spun or co-extruded components configured in a core component-sheathcomponent cross-sectional geometry, wherein the core component comprisesa thermoplastic elastomer capable of forming a physically-crosslinkednetwork and the sheath component comprises a polyolefin capable oftransitioning in response to a thermal stimulus, and wherein the fibercan be deformed from an original shape, retain a temporary shape andsubsequently return to its original shape in response to a thermalstimulus.
 3. The fiber or film of claim 2, wherein the core componentcomprises a thermoplastic elastomer.
 4. The fiber or film of claim 3,wherein the thermoplastic elastomer comprises a styrenic blockcopolymer.
 5. The fiber or film of claim 4 wherein the styrenic blockcopolymer is selected from the group consisting ofpoly(styrene-b-butadiene-b-styrene) (SBS),poly(styrene-b-isoprene-b-styrene) (SIS),poly[styrene-b-(ethylene-co-propylene)-b-styrene] (SEPS), andpoly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS).
 6. The fiber orfilm of claim 1, wherein the sheath component comprises a linear lowdensity polyethylene (LLDPE).
 7. The fiber or film of claim 1, whereinthe core component comprises SEBS and the sheath comprises LLDPE.
 8. Thefiber or film of claim 1, wherein the sheath component and the corecomponent are present in the fiber in a w/w ratio having a rangeselected from the group consisting of 95/5 (sheath/core), 90/10, 85/15,80/20, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 45/55, 40/60, 35/65,30/70, 25/75, 20/80, 15/85, 10/90, and 5/95.
 9. The fiber or film ofclaim 8 wherein the core component and the sheath component have a w/wratio of about 40/60 (sheath/core),
 10. The fiber or film of claim 2,comprising three co-spun or co-extruded components configured in aninner core component-outer core component-sheath componentcross-sectional geometry, wherein at least one of the core componentscomprises a thermoplastic elastomer and the sheath component comprises apolyolefin, and wherein the fiber can be deformed from an original shapeand return to the original shape in response to a thermal stimulus. 11.The fiber or film of claim 10, wherein the inner core component/outercore component/sheath component comprise LLDPE/SEBS/LLDPE.
 12. The fiberor film of claim 2, wherein the fiber or film returns to the originalshape within about 5 sec after being exposed to a thermal stimulus. 13.The fiber or film of claim 2, wherein the fiber or film returns to theoriginal shape within about 2 sec after being exposed to a thermalstimulus.
 14. The fiber or film of claim 2, wherein the fiber or filmexhibits a repeatable shape recovery.
 15. The fiber or film of claim 2,wherein the fiber or film is capable of deforming to at least about fourtimes an original length.
 16. The fiber or film of claim 2, wherein thesheath component has a melting point lower than the upper glasstransition temperature point of the network-forming core component. 17.The fiber or film of claim 16, wherein the core component has an upperglass transition temperature in the range from about 90° C. to about140° C.
 18. The fiber or film of claim 2, wherein the core componentfurther comprises one or more additives.
 19. The fiber or film of claim18, wherein the additive comprises a long-chain alkyl compound.
 20. Thefiber or film of claim 18, wherein the core component comprising one ormore additives has an upper glass transition temperature higher than thecore component not having the additives.
 21. An article comprising afiber or film of claim
 1. 22. The article of claim 21, wherein thearticle comprises a thermal actuator in a deployable device.
 23. Thearticle of claim 21, wherein the article is selected from the groupconsisting of a diaper, a waist band, a stretch panel, a disposablegarment, a medical or personal hygiene article, and a filter.
 24. Thearticle of claim 21, wherein the article is selected from the groupconsisting of a hinge, a truss, an antenna, a solar panel, and anoptical reflector.
 25. The article of claim 21, wherein the article isselected from the group consisting of a form fitting material,self-sealing packaging, a smart textile, and an intelligent fiber. 26.The article of claim 21, wherein the article is selected from the groupconsisting of a wound closure suture, a vascular stent, a bone-settingsleeve, and a drug delivery device.